This invention relates generally to reflectors for transforming the polarization of EM waves and more particularly to a log-periodic, three-dimensional lattice reflector for transforming the polarization of EM waves independently of the frequency of the waves and, therefore, over a wide bandwidth of operation.
The polarization of a plane EM wave is a vector and thus comprises two vector components. Existing polarization-transforming reflectors use polarization-sensitive structures such as wire grids, parallel-plate arrays, or inhomogeneous dielectric configurations. These structures are arranged so that the reflective path for one of the two vector components of a polarized wave has a different length than that of the second vector component. This difference in the reflective path lengths of the two components results in a difference in phase between the two components of a reflected EM wave. This phase-difference causes the polarization of an incident wave to be transformed into a different polarization when the wave is reflected. A disadvantage of this technique is that the path-length difference is related to the wavelength and, thus, is sensitive to the frequency of a polarized wave. Therefore, existing reflectors cannot operate over a wide bandwidth of frequency.
This disadvantage is significant, for example, as it applies to antennas for radar systems on naval vessels. because of the wide RF bandwidth among such radars, each of many such radars has its own dedicated antenna. This invention provides a means, for example, for conducting signals over a wide bandwidth from many radars to one antenna, thereby reducing the number of antennas on naval vessels.